DIY Water Treatment Train/Tower

Other great reads on Instructables:

https://www.instructables.com/DIY-Water-Treatment-Train/

https://www.instructables.com/DIY-Water-Treatment-Tower/

Author states:

I work professionally in the water treatment industry and maintain some water-centric hobbies. Knowing that I tinker in small-scale, inexpensive versions of industrial equipment, friends have asked how they might build their own systems for their hobbies or businesses - for rainwater harvesting, aquaponics, aquaculture, aquariums, and even industrial stormwater treatment. My Instructables about DIY aquatics equipment are meant to share some of the hacks, science, and builds more broadly with others.

This is a great entry, thanks.
What do you use as the 'active media"?

I think the active media is activated carbon / activated charcoal.  This can be made DIY if you want. Many how-to guides online with their own slight variations.

Example:
https://homesteadsurvivalsite.com/make-activated-charcoal/

In theory the heat source could be wood or solar.  I think basically any common salt would work, as long as the solution is concentrated enough.  The salt could even be reclaimed/recycled if desired using evaporation/distillation.